Often bone fractures are immobilized and the bones are tensioned by a wire or cord bringing the break closed so the healing of the fracture can occur by new bone growth. Typically, a wire or metal cord or cable is used as a binding. These bindings are generally wound around the break and tensioned and crimped to hold the break in close contact to allow the break to fuse with new bone growth. Ideally, fractures fuse in three months or less. In some cases up to one year. It is therefore essential the binding stays under tension for at least the typical three months, if not for at least a year.
The metals of the wire or cord are typically stainless steel or other alloy that does not corrode in the body. Attempts to use flat braided nylon bindings is disclosed in US 2012/0272816 A1 to allow accommodations of soft tissue attachment to bound bone fractures. In this disclosure it points out braid loses a significant amount of its tensile strength and under relaxation when gaps in the braid expand in contact with living tissues.
In bone surgeries, such as for fixation (i.e., fusion and unification of bones) of repositioned bones after bone fracture, e.g., fracture of the spine, bone grafting, and the like, the bones, in order for their fixation, must be kept tightly held together, so that they may not be dislocated before their fusion is completed. For this holding, steel wires have long been used, along with, depending on situations, a variety of devices such as metal, plates, rods, hooks, bolts (pedicle screws) and the like. However, flat cables formed by braiding ultra-high molecular weight polyethylene fibers (molecular weight: not less than 400000), a type of polyethylene fibers, namely high strength fibers having high tensile strength and high tensile modulus of elasticity, have recently come to be widely used for tying bones, in place of steal wires, taking advantage of their high strength and flexibility. Flat cables are used for soft tissues, such as ligaments.
However, it has been found that ultra-high molecular weight polyethylene fiber is a material that degrades. Braiding fine fibers of ultra-high molecular weight polyethylene revealed that degradation and accompanying decline in strength are more likely to proceed if the flat cables contact with living tissues on the flat cables' surface which is widened due to expansion of their inter-fiber gaps.
Conventional flat cables formed by braiding ultra-high molecular weight polyethylene fibers shrink in their cross section area when a tensile force is applied to them, because the fibers are pulled to come into close together and their degree of congestion is increased, whereas in a relaxed state when they are released from the tensile force, their cross section expands because of expansion of the gaps between the fibers and decrease in the degree of their congestion. It was confirmed increased contact of individual fibers with the living tissues, degradation of the fibers become faster when the cross section area of flat cables is expanded than when the cross section area of the flat cables is shrunk. Flat cables made of ultra-high molecular weight polyethylene fibers, when tied to bones in the body, are usually under a tensile force, but as the levels of the tensile force vary depending on the posture and motion of the body, there are also some occasions at which some part of the cable turns into a relaxed state. When relaxed and a cross section of the flat cables expands, with the gaps between the fibers expanding, the fibers come into wider contact with living tissues, thereby becoming more susceptible to degradation. This is still more important where the flat cables are applied to soft tissues, for which strong fastening is avoided. Therefore, it is desirable that surgical flat cables to be used in tying bones or suturing soft tissues like ligaments is those whose cross section area expands only a little even in a relaxed state. However, it was practically very difficult to produce such flat cables by braiding fibers.
So braided cables, while accommodating soft tissue, is clearly less than an ideal solution. Smooth steel or metal wire tensioned and crimped around the bone fracture strangulates the periosteal blood vessels surrounding the bone killing the tissue around the entire 360 degree circumference of the bone.
It is therefore an objective of the present invention to provide a bone binding construct capable of securing the bone fracture while avoiding or greatly minimizing damage to the underlying blood vessels on/in the periosteal tissue. These and other objectives are achieved by the invention as described below.